What Happens During the First Week of Pregnancy?
In the first week of pregnancy, the symptoms of pregnancy are very subtle. Most women would only suspect that they are pregnant when they miss their period, perhaps, accompanied by slight nausea, moodiness, headaches and tiredness. Of course these symptoms are very subtle, and can easily be dismissed as symptoms of stress at work. However, if a woman is sexually active, she should be highly aware and sensitive toward such symptoms, and once her suspicions are triggered, she should go to the nearest pharmacy to purchase a pregnancy test kit and use it as soon as possible. If the pregnancy test kit shows a positive result, she should make a visit to the doctor to confirm the pregnancy.

Usually the ovum is fertilized in the ampulla portion of the fallopian tube. As a result, the zygote is formed with complete genetic makeup. Depending on the combination of sex chromosomes (XX-Female or XY-Male), the sex of the foetus is determined. However, if the zygote divides to form two separate embryos, a twin pregnancy can be expected.

Soon after fertilization, a series of cells divisions take place as they progressively move towards the uterus. Such migration from the site of fertilization to the uterus may take up to 2 weeks after fertilization. The embryo, placenta and the membranes that surround the growing embryo are all specialized tissues generated from these cells. About 10 to 14 days after fertilization, the blastocyst adheres itself to the endometrium wall of the uterus.

Once the implantation takes place, the placenta provides essential nourishment to the growing embryo via the blood vessels from the mother. The hCG hormone used to detect pregnancy in urine pregnancy tests is also produced by the placenta. However, if the implantation does not occur, the tissues will be washed out with the next menstrual cycle.

Symptoms of First Week of Pregnancy
Most of the women are not even aware if they are pregnant during that first week of pregnancy. One of the earliest symptoms of pregnancy could be a missed period coupled with uncommon fatigue, headaches and mood swings caused by hormonal changes in the body. Most of the other signs of pregnancy such as tenderness of breasts and morning sickness would only start in the second week of pregnancy.

Implantation spotting which is characterized by scanty brownish discharged, unlike the normal menstrual bleeding may be present after the blastocyst attaches itself to the uterine wall.

The most sensitive pregnancy tests can potentially detect human chorionic gonadotropin or hCG levels at as low as 20 mIU. This level of hCG is present in the urine of pregnant women at about 7 to 10 days past ovulation.

References
1) Foetal Development Month by Month, reviewed by Dr Louise Chang MD

2) “Current knowledge of the aetiology of human tubal ectopic pregnancy”. Shaw JL, Dey SK, Critchley HO, Horne AW (January 2010).

3) Fetal development: First Trimester Week 1 by Mayo Clinic Staff

4) The Obstetrics Textbook by Mudaliar 9th edition
http://www.brighthub.com/health/womens-health/articles/94041.aspx

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